Crystal structure

Diamonds typically crystallize in the cubic crystal system and consist of tetrahedrally bonded carbon atoms. Lonsdaleite is a polymorph of diamond (and a distinct mineral species) that crystallizes with hexagonal symmetry; it is rarely found in nature, but is characteristic of synthetic diamonds. A cryptocrystalline variety of diamond is called carbonado. A colorless, grey or black diamond with a tiny radial structure is a spherulite.

The tetrahedral arrangement of atoms in a diamond crystal is the source of many of diamond's properties; graphite, another allotrope of carbon, has a rhombohedral crystal structure and as a result shows dramatically different physical characteristics—contrary to diamond, graphite is a very soft, dark grey, opaque mineral.